Technological application potential of polyethylene and polystyrene biodegradation by macro-organisms such as mealworms and wax moth larvae

Multiple recent reports showed accelerated biodegradation of polyethylene by employing macro-organisms such as mealworms (Tenebrio molitor) and larvae of the greater wax moth (Galleria mellonella), which seemingly chew and digest the plastic. Nevertheless, doubts regarding analytical data were published, and results are not universally transferrable. This paper aims at gaining mechanistic insights and exploring the technological prospects of potential future optimized biodegradation. We used a variety of experimental setups with both species, using both live specimens and homogenated paste, to cover a broad spectrum of potential technological setups, and performed gravimetric, microscopic and spectroscopic analyses. Live larvae showed a preference for specific substrates, yet we argue by comparison to other food sources, evidenced also by energetic uptake, that a diet of LDPE is insufficient for growth. We did not detect mass loss when homogenate paste is brought in contact with LDPE films, nor significant traces of ethylene glycol. We demonstrated that the morphology of the substrate changes after contact with live larvae, indicating some plasticizing action by an excreted liquid. This indicates a mechanism of degradation involving more than the gut microbiome alone. Using streamlined life cycle assessment and techno-economic analysis (LCA/TEA) methods, we showed that the application of these findings as either a remediation or management technology for waste plastics is highly unlikely, given the conversion to microplastics, the absence of valuable products, and the high energy cost. However, the conversion mechanism should be further elucidated for bio-functionalization of liquid alkanes as high-value application, or to mitigate plastic anomalies in composting/digesting food waste.